1. Field of the Invention
This invention relates to counterbalancing hinges and door assemblies employing such hinges, and in particular to torque rod operated hinges which counterbalance non-vertically hinged doors which must be lifted against the force of gravity.
2. Description of Related Art
There are numerous applications in which the hinge line for a door or other object is non-vertical. Such applications include, among others, hatch covers for roof openings, flush-mounted sidewalk doors, and, as illustrated here, the entrance doors for exterior basement entrances. Because the hinge line is at least partially horizontal in such applications, the weight of the door must be supported until the center of mass of the door is raised over the hinge line.
Doors of the type described are often quite heavy, and can be dangerous due to their tendency to close rapidly and with great force when released Accordingly, it has long been the practice to counterbalance the doors, not only for increased safety, but also to permit the door to be opened and closed more easily with less force.
Typically, the required counterbalancing torque has been derived from torque rods, springs or gas cylinders. Torque rods have the particular advantage that they provide their counterbalancing torque as a result of the rotation of one end of the rod relative to the other. Thus, prior art counterbalancing hinges employing torque rods simply connected one end of the torque rod to one leaf of the hinge (or directly to the door) and the other end to the other leaf of the hinge (or the door frame). Through appropriate selection of the torque rod dimensions this provided a simple means for partial counterbalancing of the door. Torque rods also have the advantages that their long thin shape can be positioned out of the way behind the door frame, and they are extremely rugged and reliable, an important consideration in doors which are often used for exterior access.
However, a torque rod (like springs and gas cylinders) provides a counterbalancing torque which is linearly proportional to the input. In the case of a torque rod, that input is the amount of the rotation or "twist" applied to it. This linear relationship means that, doubling the amount of twist applied to the torque rod doubles the counterbalancing torque it provides. Unfortunately, a non-vertically hinged door requires a counterbalancing torque which is not a linear function of the opening angle of the door, but is a sinusoidal function (sine or cosine or a shifted version thereof depending on how the opening angle is measured).
As a result, a prior art counterbalancing hinge using torque rods could only provide exact counterbalance for the door at two different opening angles, i.e., where the linear graph of applied torque (measured at the hinge line) intersects the sinusoidally curved graph of the required counterbalance torque. While these two points (which correspond to specific opening angles for the door) are under the hinge designer's control, they have usually been selected to be at approximately the fully-opened and fully-closed positions. Except at these two angles, the door is either under- or over-balanced and will move if released. Thus the counterbalancing problem is only partially solved in prior art torque rod operated counterbalancing hinges.
Bearing in mind these and other deficiencies of the prior art, it is therefore an object of the present invention to provide a new and improved torque rod operated counterbalancing hinge and door assembly which substantially completely counterbalances the door. An other object of the invention is to provide a counterbalancing hinge with a reduced number of components thereby reducing the cost and permitting faster and easier assembly.